HI-LO BI-track system

ABSTRACT

The HI-LO BI-TRACK SYSTEM uses two interleaved tracks to move railroad trains through a curve; one track is for freight trains, the second track for passenger trains. The LO-TRACK, bearing slow-speed trains, is constructed with superelevation appropriate for freight trains. The HI-TRACK, bearing high-speed trains, is constructed with superelevation to suit passenger trains. High-speed switches are installed at each end of the curve to position a train on the correct track for its speed. In general, a passenger tram would be switched to the high-speed track and a freight train would be switched to the low-speed track.

BACKGROUND OF THE INVENTION

The operation of high-speed passenger trains on the same right-of-way as conventional freight trains is problematic. In the case of an existing line, the superelevation of the outer rail in a curve is designed to suit the operating speed of a typical freight train. In practice, the actual superelevation provided is somewhat less than that required to balance centrifugal force at the normal operating speed. In this way, unbalanced centrifugal force moves the train towards the outer rail on the curve and also provides additional vertical load on the wheels running on the outer rail, thus reducing the risk of derailment from wheel-climb, A passenger train running through the same curve as described above must reduce speed to avoid overturning and to minimize passenger discomfort, i.e. being thrown across the car. Typical specifications for passenger trains call for maximum lateral acceleration of 0.1 g. This translates to a maximum allowable unbalanced superelevation, or cant deficiency as it is generally described, in the order of 4 to 6 inches for standard gauge track of 4′-8½″ between rails. Train speed must be limited on curves to a value which results in the specified cant deficiency not being exceeded and the corresponding lateral acceleration being no more than 0.1 g.

A passenger train itself is capable of running through curves at speeds that result in cant deficiencies in the order of 10 to 12 inches, with corresponding lateral acceleration significantly in excess of 0.1 g. The risk of overturning is the practical limit. One approach to this problem has been the design and construction of the “tilting train”, where the passenger compartments of the train can be rotated through 7 or 8 degrees with respect to the track, thus compensating for 7 or 8 inches of cant deficiency as far as the passengers are concerned. (For standard gauge track, degrees of tilt and inches of superelevation, or cant deficiency, are essentially the same numerically.) In this way, passengers are not subjected to unacceptable lateral accelerations while the train runs through curves at significantly higher speeds than otherwise possible.

The ability of the track to withstand the higher vertical and lateral loads on the outer rail of curved track due to the operation of “tilting trains” is being questioned today. The recent derailment at Hatfield in the United Kingdom, where the outer rail suddenly shattered into many pieces as a passenger train traveling at 110 mph ran through a curve at a high cant deficiency condition has resulted in increased attention being given to the wheel/rail interface. Train operation on curved track is a matter of concern today generally.

The “tilting train” concept permits passenger trains to run through curves at higher speeds than conventional trains. However, the possible adverse effect on the track, combined with the increased risk of overturning, may well negate any benefits achieved by the tilting configuration. The increased cost, weight and complication of the “tilting train” are additional factors to be taken into consideration.

Clearly, the ideal solution to the problem of operating high-speed passenger trains and conventional freight trains between two points is to have one track, or tracks, with superelevations on curves to suit the high-speed passenger trains and a separate track, or tracks, with superelevations on curves that correspond with the requirements of the freight trains. Unfortunately, in the real world, this ideal solution may not be practical because of space limitations and/or economics.

The HI-LO BI-TRACK SYSTEM provides the benefits of the ideal solution described above without major increase in right-of-way space at reasonable cost. It is assumed that line capacity is available in the case where high-speed passenger trains are to be added to an existing route that currently operates only freight trains, and where space requirements and/or the cost of an alternative high-speed only line make the additional line impractical. In this case, the HI-LO BI-TRACK SYSTEM allows both high-speed passenger trains and conventional freight trains to operate under the optimum conditions for both technologies.

SUMMARY OF THE PRESENT INVENTION

The HI-LO BI-TRACK SYSTEM was inspired by the gauntlet track arrangement that is used in double track systems where space is restricted laterally for a short distance. For example, gauntlet tracks are used to cross bridges that had been constructed for single track operation originally. In a gauntlet track, one line is interleaved with the opposing line so that only slightly more lateral space is required than for a single track. The advantage of the gauntlet track arrangement is that two switches are not required, as would be in the case if the two tracks converged on a single line, passed through the space-limited region, and then diverged back to double track. The only requirement for the gauntlet track is the provision of frogs where one rail of one line intersects one rail of the opposing line.

The HI-LO BI-TRACK SYSTEM uses the gauntlet track configuration in a different way and for a different purpose. In the HI-LO BI-TRACK SYSTEM, freight trains and passenger trains move on two interleaved tracks. The LO-TRACK, bearing the slow-speed trains, is constructed with a superelevation appropriate for freight trains and the HI-TRACK, bearing the high-speed trains, is constructed with a superelevation to suit high-speed passenger trains. High-speed switches are installed at each end of the curve to position a train on the correct track for its speed. In general, a passenger train would be switched to the high-speed track and a freight train would be switched to the low-speed track. Occasionally, a slow-running passenger train would be switched to the LO-TRACK and a fast running freight train might use the HI-TRACK if its speed were to be high enough, which could be the case for a mail and/or express freight train.

GENERAL DESCRIPTION OF THE DRAWINGS

The interleaved arrangement of the HI-LO BI-TRACK SYSTEM is shown in FIG. 1.

The cross-section of the HI-LO BI-TRACK SYSTEM is shown in FIG. 2.

The arrangement shown in both figures is for a right-hand curve. The arrangement for a left-hand curve would be a mirror image.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, the leading straight track, 1, is a single track used for both high-speed and low-speed trains. The leading straight track, 1, is divided at the first high-speed switch, 2, and becomes two interleaved tracks, 3 and 4. The two interleaved tracks, 3 and 4, traverse the curve and then converge at a second high-speed switch, 5, into a single trailing straight track, 6.

In FIG. 2, the LO-TRACK, 7 and 8, with superelevation appropriate for freight trains, 9, is shown on the right and the HI-TRACK, 10 and 11, with superelevation to suit high-speed passenger trains, 12, is shown on the left. Potentially, the entire rail line could be constructed with interleaved tracks and high-speed switches would be unnecessary; however, the preferred design employs a common track for both high and low speed travel on the tangent track sections.

The System must be compatible with both high-speed passenger trains and conventional freight trains with both operating at normal line speeds wherever possible. Typical requirements would include passenger trains running in the range 90 to 110 mph and freight trains running in the range 45 to 55 mph. Special circumstances, such as severe grades and/or curves might limit all trains to lower speeds. The system can be designed to suit any practical ranges of train speeds.

There are fundamental safety issues involved with the operation of trains on curved track. The first limitation is the risk of overturning outwards due to excessive speed. The second limitation is the possibility of overturning inwards in the event of a train stopping on a curve that has significant superelevation. This second limitation is particularly important for freight trains because of the risk of “string-lining” when a stopped train re-starts. The second limitation also determines the maximum safe superelevation for passenger trains that might also stop on a curve. The requirement in this case is that the wheels on the outer rail must not be completely unloaded. “String-lining” is not likely to be a problem for passenger trains.

The System must be designed such that the rails of one track do not impinge on the clearance diagram of a train on the other track. The clearance between the rails and the clearance diagram of a train on the other track should be made as large as possible in order to reduce the risk of contact with an out-of-gauge item on a passing train.

There are four possible techniques for implementing the system, each with its own advantages and disadvantages. These techniques are: Extended wooden ties with built-up outer ends, Special steel ties with raised outer ends, Special concrete ties with raised outer ends and Reinforced concrete “slab track.”

In the preferred embodiment, a high-speed switch is used at each end of the HI-LO BI-TRACK SYSTEM to direct a train on to the correct HI-TRACK or LO-TRACK as necessary at the beginning of the curve and to return the train back to the tangent track at the end of the curve. A conventional blade type of switch should be appropriate in this application. It is to be noted that frogs are not required because the rails do not intersect at any point. An alternative to the blade switch would be some form of track slewing mechanism that could connect to either the HI-TRACK or the LO-TRACK. Such a mechanism would inevitably create a small gap in the track at the junction between the slewed track and the HI-TRACK or the LO-TRACK. Such a gap could be a source of trouble in a number of respects.

The appropriate superelevation for a given curve and speed of travel can be calculated by a person knowledgeable in the art by use of the laws of physics.

-   -   For the HI-TRACK     -   Maximum superelevation relative to LO-TRACK 12″     -   Maximum superelevation relative to level ground 15″     -   Maximum operational cant deficiency 6″

For the LO-TRACK

-   -   Maximum superelevation relative to level ground 6″     -   Maximum operational cant deficiency for freight trains 4″     -   Maximum operational cant deficiency for passenger trains 6″

On conventional track, high-speed passenger trains, that can operate in the speed range 90 to 110 mph on tangent track, must slow progressively and approach the speed of the freight trains (45 to 55 mph) through curves as the curvature increases. With the HI-LO BI-TRACK SYSTEM in use, passenger trains can travel at higher speed through curved sections of track.

Calculated values of maximum speed that result in lateral acceleration of 0.1 g are given in Table 1 for a range of curves from 1 to 5 degrees. These calculations assume superelevations for the LO-TRACK that balance at 45 mph and superelevations for the HI-TRACK that balance at 90 mph. If the required superelevation for balance exceeds the maximum value specified above, then this maximum value has been used in the calculation. TABLE 1 MAXIMUM SPEED FOR CURVATURE (MPH) CONDITION 1° 2° 3° 4° 5° LO-TRACK 4″ cant def. 90 71 64 59 55 LO-TRACK 6″ cant def. 105 81 71 65 60 HI-TRACK 6″ cant def. 110 110 103 89 80 NOTE: 1. Maximum curvature for 110 mph running is 2.62°. 2. Calculations based on maximum superelevations above.

The calculations show that the System is not required for curves of less than I degree magnitude. (Degrees of curvature describe the angle subtended by a 100 foot arc.) The calculations show that the System allows lull speed of 110 mph to be maintained on curves up to 2.6 degrees magnitude for passenger trains, whereas speed would need to be reduced for all curves of 1 degree and above otherwise. The amount of speed reduction is much less with the HI-LO BI-TRACK SYSTEM in place than without it for curves in the range 3 to 5 degrees.

Adoption of the HI-LO BI-TRACK SYSTEM permits creation of high-speed lines for passenger trains over existing freight train rights-of-way without compromising the performance of either train technology. It allows 110 mph operation on curves up to 2.6 degrees magnitude. It allows 90 mph operation on curves up to 3.9 degrees magnitude. It allows 80 mph operation on curves up to 5.0 degrees magnitude. It provides major reduction in typical train travel times due to greatly reduced need for speed reductions at curved sections of track. It provides savings in energy consumption due to less braking for curves and subsequent acceleration to line speed. It provides better performance than “tilting trains” in reducing typical train travel times. It avoids high forces on the track resulting from the operation of “tilting trains.” It applies to high-speed mail and/or express freight trains in addition to high-speed passenger trains. It can be installed incrementally on existing routes, with the severe curves being improved first. 

1. A HI-LO BI-TRACK SYSTEM comprising: a first set of curved railroad track, wherein the superelevation of the first set of curved railroad track is appropriate for high-speed travel through the curve, and a second set of curved railroad track, interleaved with the first set of curved railroad track, wherein the superelevation of the second set of railroad track is appropriate for low-speed travel through the curve.
 2. The HI-LO BI-TRACK SYSTEM of claim one further comprising: a length of straight railroad track and a high-speed switch, wherein the length of straight track is joined to the first set of curved railroad track and the second set of curved railroad track by the high-speed switch.
 3. The HI-LO BI-TRACK SYSTEM of claim one, wherein the maximum superelevation of the second set of curved railroad track, relative to level ground, is 6 inches, the maximum superelevation of the first set of curved railroad track relative to second set of curved railroad track is 12 inches.
 4. The HI-LO BI-TRACK SYSTEM of claim one, wherein, and the maximum superelevation of the first set of curved railroad track relative to the ground is 15 inches.
 5. The HI-LO BI-TRACK SYSTEM of claim one, wherein, the interleaved track is supported by reinforced concrete. 